Imagine one day—the silent mode of a phone is automatically activated in order to avoid disturbing a user's sleep when the phone is placed near the bed. Likewise, favorite songs are streamed to speakers whenever the phone is placed near a stereo or a predefined timer/reminder is set if the phone is near a medicine cabinet. This kind of applications is known as context-aware computing or indoor geofencing which provides a natural combination of function and physical location. However, such a function-location combination is still not pervasive because smartphones are yet unable to sense locations accurately enough without assistance of additional sensors or installed infrastructure.
Existing localization systems are restricted from providing this type of functionality for two reasons. First, they usually rely on passively recorded WiFi, FM, or background acoustic signals, and can hence only achieve about room-level or meter-level accuracy. Nevertheless, the above-mentioned applications need more accurate location sensing, e.g., both streaming music and setting silent mode might take place in the same room or even on the same table. Second, more accurate (i.e., with error of a few cm) location sensing with light recording or acoustic beacons requires a pre-installed infrastructure. The cost of such an infrastructure and the ensuing laborious calibrations make its realization expensive or difficult, especially for personal use.
In this disclosure, a location sensing system is introduced, called EchoTag, which enables phones to tag and remember indoor locations with finer than 1 cm resolution and without requiring any additional sensors or pre-installed infrastructure. The main idea behind this system is to actively render acoustic signatures by using phone speakers to transmit sound and phone microphones to sense its reflections. This active sensing provides finer-grained control of the collected signatures than the widely-used passive sensing. Moreover, this active sensing only relies on built-in sensors available in commodity phones, thus facilitating its deployment. This fine-grained location sensing technique can enable many important/useful applications that have not yet been feasible due to large sensing errors or lack of installed infrastructure.
This section provides background information related to the present disclosure which is not necessarily prior art.